Medion 42" plasma not turn on

[forgonati]

Hi guys, i'm new in the forum, i need help with my old plasma. Sorry for my bad english, i'm a hungarian, so be forgiving with me I got this tv from my friend, its a Medion MR5265. I can't found any info on the web from this tv, sadly, but this tv uses the same one PSU, than the Planar PDP42B.

The problem is, when i turn the tv on with main switch, the red light comes on, so the standby circuit is OK. When i try it turn on with the RC, i hear clicking, the green LED comes on, the red goes off. After 3 sec, i hear clicking again (relays falls) the green LED goes off, and the red comes on, the tv is return to the standby mode.

The PSU is a Powerwel PW-1450. My opinion is, the PSU goes to the protected mode, bud i don't know, why. I checked the electrolytic caps, they looks good. I checked the output voltages which goes to the other boards, 5V, 5.5V, 15V, 12V, they are present.
I have no idea, what's wrong. Maybe the input buffer caps? They are 3x 450V 220uF brand SAMWHA. Or the output caps? They are 3x 250V 560uF. I also checked the Vs coil, but i don't see nothing, any bulging, any discoloration.

Any idea? Any help would be appreciated.

[PlainBill]

Re: Medion 42" plasma not turn on

Sorry about my poor English, I'm an American.

There are three possible reasons for these symptoms.

1. The power supply is unable to produce all the voltages. These include not only the voltages you mentioned, but also Va, Ve, Vs, Vscan, and Vset.

2. One of the Sustain boards is loading a power supply or in some cases, has blown a fuse.

3. The small signal board (also called the main miscellaneous board, or the main control board) is unable to produce one of the voltages it requires.

This has been said many times, pictures help us help you. My signature contains links on taking good pictures and attaching them.

PlainBill

[forgonati]

Re: Medion 42" plasma not turn on

Thanks for the quick reply.

I attached some pictures of the PSU, i hope that helps.

How i can check these voltages (Va, Vs, etc.)? Only with scope?

I checked all the fuses which i can find, these fuses are all OK. Sadly, i don't have service manual from this model, i can't find anything on the web from this tv

But i have schematic from the PSU.

[forgonati]

Re: Medion 42" plasma not turn on

UPDATE:

I uploaded some new pictures, on this board i find 3 broken or missing ceramic caps, it's possible that these caps causes the problem? Or the tv from this should work independently?

[PlainBill]

Re: Medion 42" plasma not turn on

UPDATE:

I uploaded some new pictures, on this board i find 3 broken or missing ceramic caps, it's possible that these caps causes the problem? Or the tv from this should work independently?

I think those caps were the victim of another fault. Those are the buffers, a problem on them often results in a failure of the sustain.

The Va, Ve, Vs, Vscan and Vset voltages are available at the connectors on the power supply. These voltages go the the sustain cards (cards with big heat sinks on either end of the chassis).

PlainBill

[forgonati]

Re: Medion 42" plasma not turn on

But these caps looks like they would be damaged because of a physical impact... Look the last picture (C12). I already saw a burned ceramic cap... These caps don't looks burned, or anything... I try replacing these caps, will see what happens.
These voltages (Vs, Va, etc.) are hunderts (or thousands) of voltages? I measured voltages on the primary side, and the secondary side of the Vs coil, nothing. These big mosfets (Q6, Q7) feeding the 3x big buffer caps, but i don't know, on what kind of frequency? Maybe 50-100kHz... Can i measure them with classic digital multimeter?

What do you think about "buffers"? These big elektrolythic buffer caps on the PSU? Or what? do you think, the Y sustain board is damaged?

Anyway, i checked again these voltages on connectors CN809, CN810, CN811. On "15V" i measured 15,2V, on "12V" 12,2V, on "5V" 5,2V, on "5V5" 5,53V. BUT. On the "32V" i measured only 24V. This may cause the problem? Please, check out the schematic of the PSU here:



THANKS

[PlainBill]

Re: Medion 42" plasma not turn on

But these caps looks like they would be damaged because of a physical impact... Look the last picture (C12). I already saw a burned ceramic cap... These caps don't looks burned, or anything... I try replacing these caps, will see what happens.
These voltages (Vs, Va, etc.) are hunderts (or thousands) of voltages? I measured voltages on the primary side, and the secondary side of the Vs coil, nothing. These big mosfets (Q6, Q7) feeding the 3x big buffer caps, but i don't know, on what kind of frequency? Maybe 50-100kHz... Can i measure them with classic digital multimeter?

What do you think about "buffers"? These big elektrolythic buffer caps on the PSU? Or what? do you think, the Y sustain board is damaged?

Anyway, i checked again these voltages on connectors CN809, CN810, CN811. On "15V" i measured 15,2V, on "12V" 12,2V, on "5V" 5,2V, on "5V5" 5,53V. BUT. On the "32V" i measured only 24V. This may cause the problem? Please, check out the schematic of the PSU here:



THANKS

Did you determine WHY 32V was low?

Why did your friend give the TV to you? Had he tried to repair it or taken it to a serviceman for repair?

Here are the problems I see at this point.

32V is low. Either something is wrong with the power supply, or something is overloading the 32V output.

Caps are damaged. I feel it might be caused by overheating, you say it looks like mechanical damage.

You are unable to give me voltage readings which might indicate the area of the problem.

There is no service information on this TV.

I don't recognize who made the plasma panel.

With those problems I am unwilling to spend any more time on this.

PlainBill

[Toasty]

Re: Medion 42" plasma not turn on

Please confirm model number MR5265. It's very odd that nothing comes up on a search.

I concur with PlainBill's statement "32V is low. Either something is wrong with the power supply, or something is overloading the 32V output."

+32v, +15v, and +12v all come from the same section of the power supply:
Transformer T2, IC11 (15v), IC12 (12v). Both IC11 & 12 draw from the 32v line.
Mind you they are simple voltage regulators. As long as the input voltage to them is above their output, and they are not overloaded, they will work and produce the 12v & 15v. So in this instance where the 32v is low, as you measured it at 24v, they will continue to work producing 12 & 15v.

You could have a problem on the input side to T2. There may not be enough "drive" to the transformer from the PFC+ which is probably around 310v. If this voltage is low, the big caps should be checked. The main cap C2 is 225uF/450v. The 3 PFC caps are C33, 35, and 36 which are 220uF/450v. Check the 18v going to the PWM, IC6.

There was also a faulty switching diode discovered in this power supply by our member maxxarcade: https://www.badcaps.net/forum/showthread.php?t=8231

Also, check out his videos:
http://www.youtube.com/watch?v=keXf05dNdSI
http://www.youtube.com/watch?v=VHZcxxDsVck

He points out 4 small caps on that little circuit board that were causing problems in the high voltage side of the power supply. The unit would shut down. Might be worth checking those out. Its right next to the big cap with the yellow label on top of it.

If everything going backwards checks out, then you need to trace the 32v line and see what is overloading it. Without a schematic, it will be darn tough to figure.

Finding other sets that use this power supply and then seeing if those service manuals are available, would be one way of seeing what that 32v line is connected to.

I do agree that the broken ceramic SMD caps look physically damaged, as if someone bumped them when reassembling the boards. The pics show all the larger caps kicked up in the air, like they were peeled up from hitting something. The solder on the edge side is visibly cracked, but the other side appears okay. When they blow off the board from a failure, there is usually some kind of burn, and I don't see that here. Also notice the rub mark on the board right at C4 in the 2nd picture. I would push the big ones back down with a small tool to hold them and then just touch each end with a soldering iron to re-secure them. The little ones will need more patience and you'll need a capacitance meter to measure them to obtain replacements.

Best of luck!

Toast

EDIT: (again) Now I looked again, and I think they got damaged when someone went to re-plug that board into the adjacent sustain board. The board overlaps the edge of the sustain, as evidenced by the connector setback in picture 1 (post 4). A misalignment when reconnecting caused the damage. Yes!!

It's a good thing! It means that something didn't go bad and cause them to blow out.

[forgonati]

Re: Medion 42" plasma not turn on

Thanks for the detailed explanation!

The model number of the TV is MR 5265. See attached photo. The logic board is from LG, also the plasma panel. The panel model is PDP42WVSN3.

So, in the T2 secondary side i measured 24V DC. The IC11 and IC12 produces voltages 15V and 12V, so they are correct. These voltages (also the 24V) going to the multiplexer IC10. Maybe the problem is there, the 24V is too low, so the PSU shuts down. Anyway, the 18V DC in the IC6 is present.

Tomorrow i check the primary side of the T2.

I checked all of diodes and rectifiers, they are OK. I checked also the output rectifiers, Those are two TO220 ultra fast dual schottky rectifiers, they are OK.

I already watched the Maxxarade's videos, and i already changed these 4 small caps, but still nothing

Anyway for the PSU i have a schematic, there:



These small ceramic caps are physically damaged, tomorrow i check these ceramic caps, and the big electrolythic caps with a capacitance meter, and i try to replace them.

THANKS

[forgonati]

Re: Medion 42" plasma not turn on

UPDATE:

New interesting thing, what i figured out: When i disconnect the Y sustain board from the PSU, so i have connected to the PSU only the Z sustain board, (other boards are connected) the PSU shuts down, and the green LED on the PSU blinks 5x. (would be good to know, what means these blinking codes) But, when i disconnect the Z sustain board, and i connect only theY sustain, the PSU don't shut down, i let it run cca. 30-40 sec, and the PSU don't shut down So maybe the Z sustain is damaged also, and overload the PSU? How can i check the sustain boards or the hybrid IC?
And one more thing, i measured the Vs, Vy and Vsetup voltages with the old analog multimeter (digital is too slow) in those connectors i have cca. 100V AC. This is correct?

Thanks

[Toasty]

Re: Medion 42" plasma not turn on

There should be a label somewhere with those correct voltages.

Also, when you pull those connectors (Y & Z), monitor the 32v line and see if it rises.

[forgonati]

Re: Medion 42" plasma not turn on

I have already tested the PSU without any other panels connected, and in the 32V connector i measured 24V, so the problem is on the PSU. Tomorrow i sheck the voltages on the primary side of the T2.

Sadly, i don't see any label with correct Vs, Vy, Vset voltages. So i don't know, these voltages what i measured, are correct or no.

What is your opinion about my last post? When i connect only the Y sustain, the PSU don't shut down. How can i test the Y and Z panel, or those hybrid ICs?

Thanks

[PlainBill]

Re: Medion 42" plasma not turn on

The first picture shows 5 labels at the top of the panel. Three of them appear to be warning labels (red). The other two labels are above the Y-Sustain and the power supply. What is on them?

The Va Ve Vs, Vscan, Vsetup voltages should be DC. I saw a rapidly pulsing voltage on one once, it was a shorted Y-sustain card.

PlainBill

[forgonati]

Re: Medion 42" plasma not turn on

You're right, i found the label, contains those voltages. Thank's a lot. See attached pic. I check those voltages one more time.

[forgonati]

Re: Medion 42" plasma not turn on

So, I checked those voltages. When i have connected all boards to the PSU, the PSU shut down after 2 sec, and i don't have enough time for testing, even with an old analog multimeter.

BUT. When i disconnect the Z sustain board, the PSU is working properly, and all voltages are present. On the "Vs" i measuring 175V, on "Vsetup" 221V, on "Va" 75,2V, on "-Vy" -80,3V. So all voltages are correct (except the 24V) But only, when i disconnecting the Z sustain board... What now??? I have a shorted Z sustain?

[PlainBill]

Re: Medion 42" plasma not turn on

So, I checked those voltages. When i have connected all boards to the PSU, the PSU shut down after 2 sec, and i don't have enough time for testing, even with an old analog multimeter.

BUT. When i disconnect the Z sustain board, the PSU is working properly, and all voltages are present. On the "Vs" i measuring 175V, on "Vsetup" 221V, on "Va" 75,2V, on "-Vy" -80,3V. So all voltages are correct (except the 24V) But only, when i disconnecting the Z sustain board... What now??? I have a shorted Z sustain?

Yes, you have a shorted Z-sustain. Looking at the first picture, you have an early LG Electronics plasma panel.

Search for (Google) the following numbers, they are the numbers of documents on Scribd. I believe the documents will provide information on the panel.

Scribd 7580885

Scribd 13287511

Scribd 19532668

You MAY have a shorted hybrid on the Z-Sustain. There should be a part number that begins with 6871

PlainBill

[Toasty]

Re: Medion 42" plasma not turn on

Ok, I got lost between you two. Is the 32v back or not...?

Does "When i disconnect the Z sustain board, the PSU is working properly, and all voltages are present." mean that the 32v is there when the Z is disconnected? You say -present- but don't say -correct-.

The statement after that makes it more confusing-
"So all voltages are correct (except the 24V) But only, when i disconnecting the Z sustain board..."

If yes, the 32v is there when Z is disconnected, then I got it.
If no, then I'm lost.



Toast

[forgonati]

Re: Medion 42" plasma not turn on

No, the 32V is still missing, i have only 24V on the "32V" connector. When i disconnect the Z sustain, i still have only 24V. But, when the Z sustain is not connected, the PSU is working perfectly, and i have all voltages, 5V, 5.5V, 15V, 12V, and i have the Vs, Va, Vy and Vsetup voltages also. And the PSU is working. The "32V" is still 24, but i think, the problem is on Z sustain board, probably i have a shorted hybid IC.

Tomorrow i check the PSU one more time, for the missing 32V, but i think, the biggest problem is, the Z sustain card overload the PSU, and send it to the protect mode... I think i must bouhgt a new board, or rebuild the shorted hybrid IC...

[Toasty]

Re: Medion 42" plasma not turn on

Okay. Then I don't understand how this means a bad Z board. If 32v is not fully up, even when everything is disconnected, then some under volt protection is probably shutting the unit down.

Toast

[forgonati]

Re: Medion 42" plasma not turn on

I don't know, really. The "32V" is only 24V, so something is wrong on the PSU, you're right.

But when i disconnect the Z sustain, the PSU is working without any problem, but when i connect it, the PSU is shut down immediately. So probably the biggest problem is on the Z sustain. Tomorrow i check the T2 primary side, and i replace those damaged ceramic caps. And i will see, what's happen.